1. Field of the Invention
The present invention relates to a separable coupling between a male component and a female component which is used with to a tool for rotationally driving a screw or a nut.
2. State of the Prior Art
Current couplings normally use conjugate male square drives and female square drives, defined for example by ISO standard 1174. The male square drive is generally integral with the head of the tool and can fit into the female square of a socket which, at its opposite end, has a driving profile designed for tightening or loosening screws or nuts. This socket may form part of a family of sockets associated with the dimension of the square drive in question. As an alternative, the male square may fit into the female square of other members such as an extension piece, a universal joint, etc.
The standardized dimensions of square drives correspond to sides 6.35 mm (xc2xc), 9.52 mm (xe2x85x9c), 12.70 mm (xc2xd) long, etc. For a given square drive, corresponding to a given tool size, the torque is limited by the mechanical strength of the male square drive This greatly limits the range of sockets that can be used. For a given threaded member, the torque required for loosening is greater than the nominal tightening torque. This amount of torque is largely unpredictable, and this unpredictability can be caused by corrosion.
As a result, if the required torque is greater than the torque capacity of the male square drive, it becomes necessary to change the tool and to use the square drive with the next size up. This assumes that several tools and several boxes of sockets are available, and leads to the use of heavier, bulkier and more expensive tools.
Various proposals have been made for increasing the torque available for a given tool and with a specific hardness of steel. However, this usually involves the use of shapes derived from a hexagon (FR-A-1,560,270 and 2,682,727, U.S. Pat. Nos. 4,512,220, 4,361,412 and 4,930,378, EP-A-0,458,771), which exhibit the drawback of being incompatible with standardized male square drives.
In addition, the known profiles are not generally designed to be equipped satisfactorily with a locking ball acted upon by a spring (as far as the male profile is concerned) or with a recess for accommodating such a ball (in the case of the female profile).
An object of the invention is to provide a coupling compatible with a standardized male square drive and making it possible, for a given size, to obtain torque which is markedly greater than that corresponding to the square drive, while being able to be equipped effectively with a ball-tppe locking device compatible with that of this square drive.
To this end, the subject of the invention is a coupling of the aforementioned type, characterized in that at least one of the two components exhibits, in transverse section, a splined profile having four straight-line segments radially on the inside, these straight-line segments together being designed to circumscribe a standardized square drive. At the corners of the square, four splines project radially outwards with respect to the contour of the square drive, the edges of which extend substantially radially. The ends of the straight-line segments are joined to the edges of the splines by rounded portions.
The coupling according to the invention may, also, have a splined profile that is substantially constant over the entire useful height of the corresponding component. Further, the female component may include, in at least one of its flat faces corresponding to the straightline segments, a recess for accommodating a locking member which is acted upon by a spring and which is borne by a flat face of the conjugate male profile or of the standardized square. Another feature is that each rounded portion of the female profile may be joined to the adjacent straight-line segment via a second rounded portion of markedly larger radius which is connected tangentially to the first rounded portion and to the straight-line segment. Further, each rounded portion of the female profile may be joined to the adjacent straight-line segment via a second straight-line segment connected tangentially to the first rounded portion and connected by a ridge to the first straight-line segment, which forms an angle of a few degrees.
The splines may be delimited laterally by edges in the form of straight-line segments or circular arcs orientated substantially radially, which connect tangentially, via rounded linking portions, to the adjacent parts of the profile. The edges of each spline may have an overall direction which is substantially radial with respect to the center of the profile. The splines may also be delimited on the outside by circular arcs belonging to circles whose centers are situated on the overall axes of symmetry of the corresponding splines. Mid-point perpendiculars of the straight-line segments pass through the center of the profile. Each straight-line segment of the female component may include a hollow section near its center, over all or part of its length. Further, the splined profile may be symmetric with respect to the two directions of rotation. Also, the splined profile may be asymmetric with respect to the two directions or rotation.
Another object of the invention is a manual or assisted tool for rotationally driving a screw or a nut. The tool has a first component designed to receive a driving torque and exhibiting a splined profile as defined hereinabove. The tool also has at least one second component for transmitting the driving torque from the first component to the screw or to the nut. This second component exhibits, within the operating clearance, a splined driving profile conjugate with that of the first component.
According to other features of such tool, the female splined profile has a constant section, whereas the male splined profile has a section which increases up to that of the female profile and then decreases, in a bi-linear or bulbous fashion. The female component has a flared entry, whereas the male component has a nose portion whose rear part is substantially frustoconical. The nose portion""s front part is substantially in the shape of a cone frustum which is more tapered and is grooved over some of its length by the inter-spline hollows of the male profile. The front part may be designed to fit partially into that part of the female profile, which is delimited by the straight-line segment. Also, the two splined profiles have similar hardnesses, especially on the order of 40 to 50 HRC.